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The Calibration FITS keywords for the primary HDU conforms to the definition
for common FITS headers with caveats pertaining to the keywords DATE-OBS,
OBJECT, OBSID, and SCAN. The caveats reflect the fact that the FITS
file is not the result of an actual observation, but rather a bench test.
Therefore, DATE-OBS's value is the day
but not the time of the most recent test,
OBJECT's value is ``NOISE DIODE,'' OBSID's value is ``calibration,''
and SCAN is 0.
In addition to the standard primary HDU keywords, the following additional
keywords will be present:
- RECEIVER
- The name of the receiver whose calibration values are in
the tables.
- MIN_FREQ
- The minimum operating frequency of the receiver and associated
feedhorn for this set of calibrations.
- MAX_FREQ
- The maximum operating frequency of the receiver and associated
feedhorn for this set of calibrations.
- NBEAM
- The number of spatially separate RF signals the receiver is
able to accept.
- TAUZENIT
- The opacity per unit air mass (for some receivers, this
may simply be a sensible default to be used until a skydip has
been performed).
- ETAL
- The rear spillover and scattering efficiency.
- APEREFF
- The aperture efficiency.
- BEAMEFF
- The main beam efficiency.
- XANGLE1
- The linear polarization angle (optional depending on recievers database).
- XANGLE2
- The linear polarization angle (optional depending on recievers database).
- YANGLE1
- The linear polarization angle (optional depending on recievers database).
- YANGLE2
- The linear polarization angle (optional depending on recievers database).
In version 2.2, all of the above quantities are assumed to be independent
of receptor, azimuth, elevation or frequency within a given receiver's
passband.
Next: Receiver Calibration Binary Table
Up: gbtMeasFits
Previous: Background
Bob Garwood
2011-07-25